usb: host: enable USB offload during system sleep

Sharing a USB controller with another entity via xhci-sideband driver
creates power management complexities. To prevent the USB controller
from being inadvertently deactivated while in use by the other entity, a
usage-count based mechanism is implemented. This allows the system to
manage power effectively, ensuring the controller remains available
whenever needed.
In order to maintain full functionality of an offloaded USB devices,
several changes are made within the suspend flow of such devices:
- skip usb_suspend_device() so that the port/hub are still active for
  USB transfers via offloaded path.
- not suspending the endpoints which are used by USB interfaces marked
  with needs_remote_wakeup. Namely, skip usb_suspend_interface() and
  usb_hcd_flush_endpoint() on associated USB interfaces. This reserves a
  pending interrupt urb during system suspend for handling the interrupt
  transfer, which is necessary since remote wakeup doesn't apply in the
  offloaded USB devices when controller is still active.
- not flushing the endpoints of actively offloaded USB devices. Given
  that the USB devices is used by another entity, unilaterally flush the
  endpoint might lead to unexpected behavior on another entity.
- not suspending the xhci controller. This is done by skipping the
  suspend/resume callbacks in the xhci platform driver.

Signed-off-by: Guan-Yu Lin <guanyulin@google.com>
Link: https://lore.kernel.org/r/20250911142051.90822-5-guanyulin@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20250911142051.90822-5-guanyulin@google.com

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